A Highly Sensitive Electrochemical Sensor For Simultaneous Detection Of Dopamine And Uric Acid Based On Graphitic-like Carbon Nitride/graphene Oxide Composite

Background:Dopamine（DA）and uric acid（UA）often coexist in human body fluids such as serum and urine,and play an important role in regulating the physiological functions and metabolic activities of the human body.Abnormal levels of dopamine may lead to many serious diseases.Clinical studies have shown that blood uric acid is correlated with catecholamine concentrations,and diseases such as schizophrenia and Parkinson’s disease have a certain relationship with the dysregulation of DA and UA.Therefore,the development of cost-effective and high-efficient analytical techniques to simultaneously monitor their concentrations can not only provide a useful reference for the clinic studies,but also play an important role in the diagnosis and prevention of these diseases.Compared with traditional analytical methods,electrochemical detection methods have the advantages of low cost,fast response and high sensitivity.The redox peaks of DA and UA easily overlap on the bare electrode,and the redox products are easily deposited on the surface of the electrode,which greatly reduces the sensing performance of the sensor.Moreover,the electrochemical response signals of DA and UA on bare electrodes are susceptible to interference by other substances.Graphitic-like carbon nitride（g-C₃N₄）not only affords more catalytical active sites for electron acceptor/donors with adjustable electronic structures,but also possesses good biocompatibility,excellent optical properties and stability.However,the electrocatalytic performance of pristine g-C₃N₄is rather limited due to its poor electrical conductivity,large contact resistance and low quantum efficiency.Graphene oxide（GO）is an important graphene derivative,and its substrate edge contains abundant oxygen-containing functional groups such as hydroxyl,carboxyl,and carbonyl.In addition to the properties of graphene,these oxygen-containing functional groups significantly improve the water solubility of GO.Therefore,GO has become an efficient catalyst support.Compared with g-C₃N₄and GO,g-C₃N₄/GO has higher catalytic activity.GO has good electron transfer ability andπ-πconjugation effect,and it can act as a good electron acceptor when coupled with g-C₃N₄.Therefore,utilizing the synergistic effect between g-C₃N₄and GO,the g-C₃N₄/GO nanocomposite is expected to achieve excellent electrocatalytic activity.Based on this,this study intends to design an electrocatalyst based on g-C₃N₄/GO composite nanosheets,in order to utilize the synergistic effect between g-C₃N₄and GO to enhance the electrochemical responses of DA and UA,thereby improving selectivity and sensitivity.Objective:1.To develop a low-cost and efficient electrochemical sensor based on g-C₃N₄/GO nanocomposite for simultaneous detection of DA and UA in human serum samples;2.To elucidate the electrochemical redox mechanism of DA and UA on g-C₃N₄/GO/GCE via combining with various electrochemical experiments.Method:1.Material Characterization:the surface morphology,crystal phase,electroactive surface area and charge transferred resistance of g-C₃N₄/GO nanocomposite were characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）.2.Electrochemical measurement:CV and differential pulse voltammetry（DPV）were used to investigate the electrochemical responses of 10μM DA and UA（1:1）on different modified electrodes.The analytical parameters such as the loading amount of g-C₃N₄/GO,accumulation potential,accumulation time,and buffer p H were optimized.The electrode kinetics of DA and UA on g-C₃N₄/GO/GCE were studied by cyclic voltammetry at different scan rates,and then the electrochemical oxidation mechanism of DA and UA on the g-C₃N₄/GO/GCE was discussed.The sensing performance for individual and simultaneous detection of DA and UA on the g-C₃N₄/GO/GCE was mainly evaluated.In addition,the anti-interference performance,repeatability,reproducibility and stability of the g-C₃N₄/GO/GCE were also investigated.3.Actual sample detection:the levels of DA and UA in human serum samples were quantitatively analyzed by DPV method using the g-C₃N₄/GO/GCE.The reliability for detecting DA and UA was further verified by the standard recovery method.Results:1.The SEM images and XRD patterns confirmed the successful synthesis of g-C₃N₄/GO composite nanosheets.The resultant g-C₃N₄/GO significantly increased the electroactive surface area and reduced the charge transferred resistance,thus effectively promoting the electron transfer process.2.The g-C₃N₄/GO significantly enhanced the electrochemical response of DA and UA.The optimal analytical parameters were g-C₃N₄/GO loading of 5μL,accumulation potential of-0.3 V,accumulation time of 150 s,and buffer p H of 3.77.3.The sensing performance of g-C₃N_4/GO/GCE for the simultaneous detection of DA and UA did almost not decrease significantly compared with their individual detections.The linear response range of the g-C₃N₄/GO/GCE for the simultaneous detection of DA and UA was 0.03–30μM.The limits of detection（LOD）for the simultaneous detection of DA and UA were as low as 4.6 n M and 5.4 n M,with sensitivities of0.04329 and 0.1064μA·μM^-1,respectively.4.The g-C₃N₄/GO/GCE exhibited excellent anti-interference performance,repeatability,reproducibility and stability.Moreover,the g-C₃N₄/GO/GCE successfully achieved the simultaneous detection of DA and UA in human serum samples with satisfactory recovery.Conclusion:The proposed g-C₃N₄/GO/GCE significantly enhanced the electrochemical responses of DA to UA,with excellent sensing performance（wide linear response range,low LOD）and selectivity.Moreover,the g-C₃N₄/GO/GCE successfully realized the simultaneous detection of DA and UA in the human serum samples.10 figures,4 tables,and 63 references...